ESTI Refines Pulmonary Nodule Management in Lung Cancer Screening

Early detection of lung cancer through low-dose CT screening in high-risk populations has proven to reduce lung cancer-specific mortality. However, risk stratifying pulmonary nodules that are detected during screening is still a clinical challenge, balancing the need for early intervention against the risks of false positives, excessive imaging, and overtreatment.

A new recommendation from the European Society of Thoracic Imaging (ESTI) aims to address this gap by refining the definition of positive, indeterminate, and negative screen results. Here’s an overview of their report.

Standardizing Risk Stratification
The ESTI recommendation enhances existing lung cancer screening protocols by placing a stronger focus on lesion aggressiveness for pulmonary nodules. The rationale among nodule management categories is the estimated risk of malignancy in the detected nodule. By standardizing these categories, the guidelines provide clinicians with a framework for risk stratification, follow-up timelines, and appropriate diagnostic interventions.

Guideline Criteria for Nodule Management
The ESTI guidelines provide specific criteria for classifying nodules based on size, volume, and morphology:

• Negative Screen (Very Low Risk): Includes nodules with benign features (calcification, fat components, typical intrapulmonary lymph node), solid nodules < 100 mm³ (< 6 mm), and non-solid nodules < 30 mm. These patients can continue with annual screening.
• Indeterminate Screen (Low to Intermediate Risk): Includes solid nodules ≥ 100 to < 250 mm³ (≥ 6 to < 8 mm) without suspicious features, or < 100 mm³ with suspicious features. It also includes non-solid nodules ≥ 30 mm. These require follow-up CT at 3 or 6 months depending on the specific characteristics.
• Positive Screen (High Risk): Includes solid nodules ≥ 500 mm³ (≥ 10 mm), or ≥ 250 mm³ (≥ 8 mm) with suspicious features. These require diagnostic work-up and referral to a Multidisciplinary Team (MDT).

Volumetry and Growth Assessment
Assessment of nodule growth and aggressiveness is key to malignancy screening, since most lung tumors exhibit exponential growth. Volumetry using the volume doubling time (VDT) is recommended to measure growth rate of solid nodules and of the solid area of subsolid nodules. ESTI highlights the usage of software-based volume measurements for precision, while acknowledging limitations:

• Manual measurements of diameter are subject to significant intra-observer (±1.4 mm) and inter-observer (±1.7 mm) variability, which can lead to the mistaken belief that a nodule is growing when it is stable, and vice versa.
• The relative difference between volumes strongly depends on segmentation accuracy. For completely segmented nodules, the 95% confidence interval for the difference between two volume measurements is approximately ±12%, but this increases to approximately ±30% for incompletely segmented nodules.

Addressing Measurement Variability
All nodule measurements are prone to variability depending on the software, nodule morphology, and scanning technique. ESTI emphasizes that the same software should be used throughout a lung cancer screening program, or at least as part of the follow-up of individual participants. If new software is installed, earlier measurements have to be repeated if management may be affected. Furthermore, acquisition and reconstruction parameters need to be kept as constant as possible during follow-up, with soft kernels preferred to achieve more accurate and reproducible volumetric measurements.

A Framework for Clinical Practice
The proposed ESTI nodule management concept refines the definition of screen results and will contribute to controlling false positives, reassessment errors, and the number of intermediate CT scans, while also reducing overdiagnosis and the risk for stage-shift during follow-up. To ensure standardization, the use of structured reports is proposed to enable consistent reporting of findings, improved communication, and reduced ambiguity. As screening programs evolve, these refined protocols offer a pathway to maximize the benefits of early detection while minimizing the potential harms of overtreatment.

Reference:

Snoeckx A, Silva M, Prosch H, et al. Lung cancer screening with low-dose CT: definition of positive, indeterminate, and negative screen results. A nodule management recommendation from the European Society of Thoracic Imaging. Eur Radiol. 2026;36(1):135-147. doi:10.1007/s00330-025-11648-4